Internal combustion engines utilizing two or more different fuels have been proposed. As one example, the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. describe engines that are capable of using multiple fuels. Specifically, the Heywood et al. papers describe directly injecting ethanol into the engine cylinders to improve charge cooling effects, while relying on port injected gasoline to providing a majority of the combusted fuel over a drive cycle. The ethanol, in this example, can provide increased octane and increased charge cooling due to its higher heat of vaporization in comparison to gasoline, thereby reducing knock limits on boosting and/or compression ratio. This approach purports to improve fuel economy and increase utilization of renewable fuels.
The inventors of the present disclosure have recognized that requiring a user to re-fuel the engine system with two or more separate fuels (e.g., gasoline and ethanol), in order to achieve the advantages described by Heywood et al., can be burdensome. To address this issue, the inventors herein have provided a method of operating a fuel delivery system for a fuel burning engine of a vehicle. The method can include: separating a first fuel and a second fuel from a fuel vapor on-board the vehicle, said fuel vapor including at least an alcohol component and a hydrocarbon component and said first fuel including a higher concentration of the alcohol component than the fuel vapor and the second fuel; condensing the separated first fuel from a vapor phase to a liquid phase; delivering the condensed liquid phase of the first fuel to the engine; and combusting at least the condensed liquid phase of the first fuel at the engine.
By separating a fuel vapor into alcohol rich and hydrocarbon rich components, the benefits of increased engine performance and/or fuel economy can be realized without requiring the vehicle operator to refuel the vehicle with two or more separate fuels. Note that these fuel vapors may be generated on-board the vehicle from an initial liquid fuel mixture through the application of heat and/or vacuum. Additionally, fuel vapors may be generated from the fuel mixture during a refueling operation or during diurnal heating or cooling of the fuel system, even when the vehicle is not in use.
The inventors have further recognized that in one approach, separation of a fuel vapor can be achieved by passing the fuel vapor through an adsorption device that adsorbs a hydrocarbon component of the fuel vapor at a higher rate than an alcohol component. However, in other examples, separation of the fuel vapor can be achieved by passing the alcohol component of the fuel vapor through a selectively permeable membrane that transports the alcohol component of the fuel vapor at a higher rate than the hydrocarbon component.
Further still, the inventors have recognized that these fuel vapors may be separated using a batch processing approach, which can enable a more continuous fuel vapor separation operation where two or adsorption devices are utilized. As one example, the inventors have provided an engine system for a vehicle that includes: an internal combustion engine including an air intake passage; a fuel storage tank; an evaporator configured to receive a fuel mixture from the fuel storage tank via a fuel passage and to vaporize a higher volatility fuel from a lower volatility fuel contained in the fuel mixture; a vapor separation system including at least a first adsorption canister and a second adsorption canister arranged in parallel; a vapor passage fluidly coupling a vapor formation region of the evaporator with an inlet of each of the first and second adsorption canisters of the separation system; a fuel vapor purging passage fluidly coupling the air intake passage of the engine with an outlet of each of the first and second adsorption canisters; and a control system configured to: operate the evaporator to vaporize the higher volatility fuel from the lower volatility fuel; and during a first mode, pass the higher volatility fuel through the first canister to adsorb a hydrocarbon fraction of the higher volatility fuel at the first canister while purging fuel vapors from the second canister to the air intake passage of the engine; and during a second mode, pass the higher volatility fuel through the second canister to adsorb the hydrocarbon fraction of the fuel vapor at the second canister while purging fuel vapors including the hydrocarbon fraction adsorbed during the first mode from the first canister to the air intake passage of the engine.
By periodically operating at least one of the adsorption devices to retain hydrocarbons of the fuel vapor while purging at least one other adsorption device of previously stored hydrocarbons, a more continuous vapor separation process can be achieved.